Malignant tumor is a cytopathy, characterized in that the normal cell division is out of control, resulting in the immoderate cell-differentiation and proliferation, invasion into local tissues and metastasis. Malignant tumors have become common diseases seriously detrimental to the life and health of human. According to the incomplete statistic data, there are about 20 million new cases per year in the world. Therefore, at present, it is the most challenging and significant area in life science to research and develop antitumor drugs.
Generally, traditional antitumor drugs are cytotoxic drugs, which have disadvantages, such as inevitable toxic and side effects, poor selectivity and resistance, etc. Various basic life processes in malignant tumor cells, such as signal transduction, regulation on cell-cycle, angiogenesis and the like, have been gradually demonstrated with the rapid progress in life science. It is an important aspect in the research of antitumor drugs to develop antitumor drugs with excellent therapeutic efficacy and low side effects by using certain key enzymes, which are relevant to the proliferation of tumor cells in signal transduction paths, as targets for drug screening. Protein tyrosine kinase is a kind of protein for catalyzing the transfer of γ-phosphate from ATP to certain amino acid residue of a protein, which plays an important role in the intracellular signal transduction path, and regulates a series of physiological processes, such as cell growth, differentiation and death. According to the information in prior art, over 50% of oncogenes and the products thereof possess protein tyrosine kinase activities, the aberrant expression of which will result in the disorder of life-cycle of cells, and, in turn, the formation of tumor. Additionally, the aberrant expression of tyrosine kinase is closely relevant to tumor metastasis and chemoresistance.
Epidermal growth factor receptor tyrosine kinase (EGFR) can modulate multiple signal transduction paths, transfer the extracellular signal into cell, and play an important role in regulating the proliferation, differentiation and apoptosis of normal cells and tumor cells (Cell, 2000, 100, 113-127). Therefore, the purpose for treating tumors can be achieved by selectively inhibiting the signal transduction path modulated by EGFR, thereby providing a feasible way for targeting-treatment of tumors. The drugs with EGFR as the target, such as Gefitinib, Erlotinib and Laptinib, have been marketed, for treating non-small cell lung cancer and breast cancer. However, according to clinical experience, resistance will occur in most of non-small cell lung cancer patients after being repeatedly treated by using Gefitinib or Erlotinib, wherein 50% of resistance cases are relevant to the mutation of one amino acid in EGFR kinase domain (threonine residue at position 790 is mutated to methionine, T790M) (The New England Journal of Medicine, 2005, 352, 786-792). For overcoming the T790M-relevant resistance, a series of irreversible ATP competitive inhibitors, such as CI-1033, BIBW2992, HKI-272, PF00299804 etc., have been clinically studied. The irreversible inhibitors have one Michael receptor fragment capable of forming a covalent bond with one conservative amino acid (Cys797) in ATP binding site of EGFR, thereby obtaining stronger EGFR-binding affinity, compared with reversible inhibitor (Journal of Medicinal Chemistry, 2009, 52, 1231-1246). However, the results from clinical experiments for the irreversible inhibitors said above are not ideal, due to the toxicity from off-target effects, side effects from low selectivity, and insufficient drug concentration in a patient in vivo, etc (Nature, 2009, 462, 1070-1074). Therefore, the development of novel irreversible EGFR inhibitors will have great clinical significance and application prospects.
B lymphocyte tyrosine kinase (BLK) belongs to a non-receptor tyrosine kinase, and is classified into Src family as c-Src, Fyn, Lck, c-Yes, Fgr, Hck, Lyn, etc. BLK is mainly expressed in B lymphocyte line, and during the whole process of B lymphocyte development, except for plasma cell phase, BLK is expressed. BLK involves in downstream signal transduction of B lymphocyte receptor (BCR) (Molecular Biology Reports, 2011, 38, 4445-4453), and affects pre-B lymphocyte receptor-related functions (Journal of Experimental Medicine, 2003, 198, 1863-1873), thereby affects differentiation and proliferation of B lymphocyte. Constitutively activated BLK expressed in Murine B cell line, T cell lines will lead to the development of B-cell lymphoma, T-cell lymphoma respectively (Proceedings of the National Academy of Sciences, 1998, 95, 7351-7356). More importantly, the ectopic expression of BLK is present in human cutaneous T-cell lymphoma (CTCL) (Blood, 2009, 113, 5896-5904), suggesting that BLK can be used as a potential target for anticancer drug. In addition, BLK gene polymorphism is closely related to pathogenesis of systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and other autoimmune diseases (The New England Journal of Medicine, 2008, 358, 900-909), and induction of apoptosis of B-cells may be an effective treatment for the above diseases (Nat Reviews Immunology, 2006, 6, 394-403).
FMS-like tyrosine kinase 3 (FLT3), which belongs to type III receptor tyrosine kinase family, plays an important role in the proliferation, differentiation and apoptosis of hematopoietic cell (Oncogene, 1993, 8, 815-822). Upon binding to FLT3 ligand, FLT3 activates multiple downstream signaling pathways, including STATS, Ras/MAPK and PI3K/AKT pathway. FLT3 mutations exist in about one third of acute myeloid leukemia (AML) patients (Blood, 2002, 100, 1532-1542), including mutations in internal tandem dupication sequences of juxtamembrane domain 14 and (or) 15 exons (FLT3-ITD), and mutations of amino acid deletion or insertion in activation loop of tyrosine kinase domain (FLT3-TKD). Moreover, high expression of FLT3 can be found in acute leukemia cases (Blood, 2004, 103, 1901), and over-expression of FLT3, FLT3-ITD mutation and FLT3-TKD mutation will lead to a poor prognosis in AML patients. Thus, FLT3 has become an important target for the treatment of AML. So far, there is no FLT3 inhibitors are approved for clinical use, and clinical effects of many FLT3 inhibitors in clinical trials are not desirable yet.
Therefore, it is a hot-spot in the research and development of anti-tumor targeted drugs to improve the clinical efficacy of small molecule kinase inhibitors, and the most promising strategy is to develop multi-target inhibitors simultaneously targeting multiple kinases associated with pathogenesis of disease (tumor).